Integrated circuits have evolved into complex devices that can include millions of transistors, capacitors and resistors on a single chip. The evolution of chip design requires faster circuitry and greater circuit density that demand increasingly precise fabrication processes.
Rapid thermal processing (RTP) generally includes heating from a radiant heat source, such as lamps and/or resistive heating elements. In a conventional RTP system, the substrate is heated to a desired temperature, and then the radiant heat source is turned off, which causes the substrate to cool. In some systems, a gas may flow onto the substrate to enhance cooling. However, as processing parameters continue to evolve, temperature ramp up and heating uniformity during RTP requires closer monitoring and control.
A frequently used process for treating substrates (also referred to herein as “wafers”) is ion implantation. Ion implantation typically takes the substrates through a thermal process performed in a rapid thermal processing (RTP) chamber that provides a uniformly distributed thermal cycle that can heat the substrate from room temperature to approximately 450° C. to about 1400° C. In a conventional RTP system, robotic arm is used to transfer substrates to a structure that supports the substrates in the RTP chamber. The substrates need to be placed on the center of the structure to promote even heat distribution across the substrate surface. However, when substrates are transferred onto the structure, it is often that the positioning of the substrate on the ring structure cannot be accurately repeated. For example, the robotic arm may not be able to position consecutive substrates onto the same centered position on the structure. The difference in the positioning of the substrates may lead to uneven heat distribution across the substrate surface, therefore a decrease in production of the substrate.
Some rapid thermal processing apparatus use a substrate support in the form of an “edge ring” to support the substrate or wafer. As the name implies, the edge ring holds the substrate, typically called a wafer, around the edges only so as to minimize the contact with the substrate. If the wafer is not centered on the edge ring or other wafer support, uneven overlap on either side of the wafer create a side to side non-uniformity that rotates with the wafer (and wafer support). Robot placement accuracy is limited to ±0.007 inches. However, for every 0.001 inch that the wafer is placed off-center of the wafer support, the wafer can experience a 1° C. side-to-side temperature difference. Thus, in order to achieve temperature uniformity in the range of ±2° C., the wafer needs to be placed on the wafer support such that the wafer and wafer support are coaxial within ±0.002 inches.
Therefore, there is a need in the art for apparatuses and methods for the micro-positioning of a substrate or for precision control of the substrate on a wafer support in a rapid thermal processing chamber.